The present invention relates to an impact hammer, particularly to the noise attenuation of a hydraulic hammer, so that the structure-borne noise is insulated in between the impact member and the side plates of the impact hammer.
A hydraulic hammer is used for instance in breaking frozen earth's crust, or in tunnel extraction in areas where the earth is softer than the bedrock. The practical applications of the hydraulic hammer lead to the fact that while using the hammer, the created noise causes problems to the environment, and particularly to the users of the hammer. Therefore various solutions have been suggested for reducing noise. One of the suggested arrangements comprises vibration-restricting rubber bits in between the protective casing and the impact member, which bits are installed in longitudinal direction with respect to the axis of the impact member. The rubber bits are so shaped that one part thereof is attached to the protective casing and the other part to the impact member. Thus the rubber bits are subjected to relatively great shearing strengths during the impact stroke, and consequently the working life of such rubber bits cannot be very long.
From the EP patent 144,282 there is known a hydraulic impact hammer where separate attenuation elements are used for eliminating noise during the use of the hammer. The attenuation elements are made of some elastic material. In order to install these attenuation elements, the protective casing of the hammer must be provided with special installation openings, or the impact member must be fitted within oversized attenuation elements. Thus the installation of the attenuation elements is cumbersome and requires special tools. Moreover, while using the hammer, bending strains are directed to the protective casing, so that the bending also causes defective extra strain to the hammer housing.
The EP patent 191,336 describes a hydraulic impact hammer where the noise caused by the use of the hammer is reduced by means of the installation arrangements of the working unit. A special feature of the hammer is that the employed attenuation elements are arranged transversally with respect to the axis of the impact member, around fastening bolts connecting the different parts of the protective casing. The employed attenuation elements are rubber collars, which, however, take up a lot of space and make the hammer rather large in size.